首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   7505篇
  免费   905篇
  国内免费   703篇
化学   1960篇
晶体学   109篇
力学   911篇
综合类   64篇
数学   2251篇
物理学   3818篇
  2024年   17篇
  2023年   206篇
  2022年   185篇
  2021年   191篇
  2020年   257篇
  2019年   217篇
  2018年   229篇
  2017年   263篇
  2016年   278篇
  2015年   235篇
  2014年   384篇
  2013年   607篇
  2012年   381篇
  2011年   592篇
  2010年   417篇
  2009年   494篇
  2008年   499篇
  2007年   470篇
  2006年   423篇
  2005年   331篇
  2004年   320篇
  2003年   295篇
  2002年   253篇
  2001年   224篇
  2000年   194篇
  1999年   143篇
  1998年   141篇
  1997年   125篇
  1996年   92篇
  1995年   75篇
  1994年   69篇
  1993年   51篇
  1992年   53篇
  1991年   61篇
  1990年   33篇
  1989年   39篇
  1988年   30篇
  1987年   34篇
  1986年   27篇
  1985年   23篇
  1984年   28篇
  1983年   13篇
  1982年   26篇
  1981年   15篇
  1980年   12篇
  1979年   13篇
  1978年   9篇
  1977年   11篇
  1976年   6篇
  1973年   10篇
排序方式: 共有9113条查询结果,搜索用时 15 毫秒
991.
We study the almost sure limiting behavior and convergence in probability of weighted partial sums of the form where {Wnj, 1jn, n1} and {Xnj, 1jn, n1} are triangular arrays of random variables. The results obtain irrespective of the joint distributions of the random variables within each array. Applications concerning the Efron bootstrap and queueing theory are discussed.  相似文献   
992.
Development of optimal coal mining and stockpiling strategies for a new 960 MW thermal power station depends strongly on the operation of New Zealand's mixed hydro/thermal power system. To overcome the large dimensionality of the problem the optimization proceeds in two phases for each future scenario studied. Phase 1 finds optimal hydro operating strategies with thermal generation in merit order of marginal fuel costs. It uses stochastic dynamic programming. The hydro generating strategies are used as input to the phase 2 stochastic simulation of the coal mining and stockpiling operation at the new thermal station. Finally, a strategy is identified which is a priori best over all future scenarios of industrial development and oil prices studied.  相似文献   
993.
H^—5的正四面体中心和正方形中心构型能量的理论计算   总被引:2,自引:1,他引:1  
文中用MACQM(modifiedarangementchannelquantummechanics)方法计算了负离子团簇H-5的正四面体中心和正方形中心构型的能量随中心原子核到顶角原子核间距离R变化的曲线。计算得知,两种构型均在R=1.55a0时有能量极小值E正四面体中心=-2.7899a.u.,E正方形中心=-2.7539a.u.。说明H-5的这两种结构都可能存在,但正四面体中心结构较为稳定。  相似文献   
994.
This note is devoted to study the exponential convergence rate in the total variation for reversible Markov processes by comparing it with the spectral gap. It is proved that in a quite general setup, with a suitable restriction on the initial distributions, the rate is bounded from below by the spectral gap. Furthermore, in the compact case or for birth-death processes or half-line diffusions, the rate is shown to be equal to the spectral gap. Research supported in part by NSFC, Qiu Shi Sci. & Tech. Found. DPFIHE, MCSEC and Univ., of Rome I, Italy  相似文献   
995.
相空间中的Noether定理及其应用   总被引:1,自引:0,他引:1  
从修改的哈密顿变分原理出发导出相空间的 Noether 定理,对正则拉氏量系统,分析该系统在相空间中的对称性质,可导出其相应的守恒量,而这种相空间中的对称性质在位形空间中常常又是不呈现出来的.对奇异拉氏量系统,该系统具有 Dirac约束,我们分析了约束系统的对称性质,讨论了 Dirac 猜想是否有效.  相似文献   
996.
Analogous to Kingman's Poisson Counts, power law counts are defined. Further, these are used to obtain the maximum likelihood estimator of the scale parameter of a power law process. Comparison of this estimator is done with those obtained by using other sampling schemes. Also, cost comparisons are done under the assumption of equal asymptotic variances under different sampling schemes.Work done while the author was with the Department of Statistics, University of Poona. Current address: Dept. of Mathematics, CME, Pune.  相似文献   
997.
In this paper we analyse a two-stage game involving the government and n agents who engage in a single activity (driving). The government establishes the legal policy setting and the agents proceed to play a non-cooperative game of incomplete information with a risk of accident in which their behavioral strategy is their level of care. We examine the Nash-equilibrium conditions for single-activity accidents between heterogeneous agents, ‘good’ drivers or ‘bad’ drivers allowing a variable damage function and a liability rule defined on the cube. The relative desirability for society of alternative equilibria and the conditions under which they can obtain are discussed. The constraints which circumscribe the ability of the government to induce an equilibrium involving careful driving are demonstrated. It transpires that when the proportion of good drivers increases, it becomes more difficult to sustain a careful equilibrium whereas an equilibrium of reckless behavior becomes easier to sustain. Various extensions of the models are also presented.  相似文献   
998.
We consider the problem of constructing entrance laws for Feller diffusions on the state space (0, ∞). Our method, based on Feller-McKean theory of one-dimensional diffusions, gives an analytic expression for the entrance density in terms of transition density. Moreover, the entrance density is the density of the first passage time to the left boundary {0}. Also, the entrance density is related to the transition density via Doob's h-path transformation.  相似文献   
999.
Precision densities and sound velocities for solutions of selected univalent electrolytes and nonelectrolytes in DMSO have been measured at 25°C, and apparent molar isentropic compressibilities and volumes evaluated. The data were extrapolated to infinite dilution to obtain standard state partial molar quantities, K s,2 ° , and V 2 ° . Values of V 2 ° and K s,2 ° for alkali metal halides in DMSO are very similar to those in water. The results confirm conclusions derived from data in water and other nonaqueous solvents that K s,2 ° and V 2 ° for alkali metal halides are strongly dependent on solvent compressibility. K s,2 ° becomes more negative and V 2 ° decreases as solvent compressibility increases. Attempts to determine ionic K s,2 ° values suggest that a significant dissymmetry exists between 4P+ and 4B in DMSO, whereas in water and MeOH, these large ions appear to behave similarly. Ionic V 2 ° values support this conclusion. Steric hindrance in the DMSO molecule is believed to be responsible for this dissymmetry.  相似文献   
1000.
P P Divakaran 《Pramana》1979,13(3):231-236
A master scaling law is proposed for arbitrary distributions in arbitrary hadronic processes of which all experimentally established scaling laws (and a host of others, easily deduced as occasion demands) are special cases.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号